Method for drilling and completing wells



Nov. 18, 1958 l R. F. wlLcox 2,360,854

METHOD FOR DRILLING AND COMPLETING WELLS Filed Sept. 1. 1955 5 Sheets-Sheet 1 fl, Ywmxwym xmwm I n "LA 80 is /06 Roy F. Wilcox INVENTOR. ,9

Ln BY ana/M 5mm Nov. 18, 1958A R. F. wlLcox METHOD FOR DRILLING AND COMPLETING WELLS 3 Sheets-Sheet 2 Filed Sept. l. 1955 INVENTOR.

Nov. 1'8, 1958 R. F. WILCQX l 2,880,854

METHOD FOR DRILLING AND COMPLETING WELLS Filed Sept. l. 1955 3 Sheets-Sheet 3 Surface g j L U37/ Z Drf//ing Flu/'d j Level Wafer Level Dr/l/ Taal Cave/.n

F/ufd 7W Level 7 y Wafer Leve/ V Mur/' Roy F. Wilcox IN VEN TOR.

United States Patent O j 2,860,854 lVIETHOD FOR DRILLING ANDYCOMPLETING 'WELLS Roy F. Wilcox, McCook,` Nebr.

Application September 1, 1955, Serial No. 532,050

7 Claims. (Cl. Z55- 1.8)

This invention relates to novel and useful improvementsA in a method for drilling and completing wells and constitutes 'a continuation-impart of my prior copending application Serial No. 197,370, led November 24, 1950, for Apparatus and Method of Drilling and Completing Wells and which has now matured into Patent No. 2,721,059, issued October 18, 1955.

The primary object of this invention is to increase drilling speed and to afford a convenient means for the is to provide a drill tool which will rotate in a single direction during vertical travel in one direction.

It is still another important object of the present invention to provide a cable-type drilling tool of the I hollow type having a valve adjacent its lower end which will not bind or stick in use, and which will reduce and break up a core upon the advance of the drill to prevent a core from jamming the valve.

Yet another important object of the present invention is to provide jars for rotatably supporting the tool which will not sand up to lock the same against free rotation.

It is also another important object of this invention to provide a method and apparatus for ascertaining the water level in a loose sanded formation or other structurally weak formation susceptible to cave-ins before casing oif the formation, so that the well need only be cased after it has been drilled to a lsuflicient depth to produce water in the desired quantities.

A very important object of the invention claimed herein is to provide a method, particularly adapted for use with cable tools, for determining with accuracy the depth at which a water level lies and thereby drill a well having apredetermined depth of water therein.

A further object is to devise a method in accordance with the preceding method, which will enable the well bore to be completed to the precise depth desired into the water table before the well casing is set.

A meritorious feature of the present invention resides in the valve and restricted non-circular throat construction at the lower end of the tool, which will prevent jamming of the valve by a core entering the lower end of the tool, with the non-circular restricted throat servfing to wear and break off such a core during the twisting @of the tool about its vertical axis.

Another important feature ofthe present invention resides in the jar constructionprovided which will not lsand. up to prevent rotation of the tool and which also Patented N0v.'1s, 195s ice affords a fluid passage through the upper end of the hollow tool.

Still another important feature of the present invention resides in the provision of a blade on the jaw construction which serves to break up material in the hollow tool.

Final important features to be specifically enumerated herein reside in theprovision iof slots in the tubular. body to afford mud circulation together with the clean-out openings and the removable cover plates therefor, such clean-out openings being adapted to be used in lieu'of the slots in the tubular body.

These, together with various ancillary features and objects of the invention which will later become apparent as the following description proceeds, are attained by the present invention, a preferred embodiment of which has been illustrated by way of example only in the accompanying drawings, wherein:

Figure l is aside elevational view of the present invention, this view showing the same in drilling position at the bottom of a well hole; j.

Figure 2 is an enlarged central vertical sectional view of the upper end of the drilling tool illustrating par-` ticularly the jaw construction shown in side elevation therein;

Figure 3 is an enlarged horizontal sectional view taken upon the plane of the section line 3 3 of Figure 2;

Figure 4 is-an enlarged vertical sectional view through the 'lower end of the-tool, illustrating particularly the restricted throat construction and the manner in which the valve plate ishingedly secured to the tool,. the open position of the valve plate lines; ,r Figure 5 is a detail view of a portion of the jar conf struction, this View showing the same in side elevation with portions broken away to show the internal construction of the same; v Figure 6 is a horizontal sectional view taken upon the plane of the section line 6-'6 of Figure 4;

Figure 7 is another horizontal sectional view of the present invention, this view being taken upon the plane of the section line 7 7 of Figure 4; A j

Figure 8 is a bottom plan view of the present invention;

Figure 9 is a perspective view of the removable closure plate used for a clean-out opening in drilling tool;

Figures 10414 vare diagrammatic views, parts being broken away, which illustrate the Various steps in the novel method of this invention in completing a well vat adesired depth into a water producing formation, and wherein;

Figure 10 is a diagrammatic view showing a well bore drilled to a depth estimated to be at a desired distance below the level of the Water table of a water producing formation; n

Figure ll is a diagrammatic view illustrating the drill raised above the water level, with the drilling fluid removed and showing the well bore caved-in by the hydrostatic pressure of the waterbearing formation upon release of the drilling fluid pressure;

Figure l2 is a diagrammatic view illustrating the lling of the caved-in well bore with drilling mud and the restoration of the drilling Huid pressure inpreparation for resumption of drilling; v

Figure 13 is a diagrammatic view illustrating theI completion of the drilling operation by continuing drilling through the 'mud to the predetermned depth below the cave-in and the water level; and

Figure 14 is a diagrammatic view showing the setting being indicated yin dotted and gravelling of the well casing, the removal of the drilling string and the completion of the well.

Reference is now made more specifically to the accompanying drawings, wherein like numerals designate :similar parts throughout the various views, and in which the drilling tool is designated generally at 10.

As best shown in Figures 1 and 4, the drilling tool 10 comprises an elongated tubular body- 12 that has secured to its lower end, as by welding 14, an annular drilling bit 16. The annular drilling bit 16 is -radially enlarged at its lower end as at 18, and isprovided with a cutting edge 120 fora purpose t-o be seen presently.

An annular valve seat 22 is disposed in the lowerend of the body l12 and is seated against the underside of a shoulder 24 therein, As best shown in Figures 4, 7 and 8, the valve seat 22 is formed with anon-circular opening 26 therein which tapers upwardly.

In `the preferred construction, the inner surface of the bit 16 is circular in transverse section and tapers upwardly and smoothly merges with the surface of welding 28 that secures the valve seat 22 to both the tubular body 12 and the bit 16. The surface of the welding 28 is likewise tapered upwardly and in turn smoothly merges with the side walls of the valve seat 22 defining the opening 26. The inner surface of the welding 28 and the side walls of the valve seat 22 defining the opening 26 are so contoured as to smoothly change from the circular form of the bit to what may be generally described as a truncated sector at the most restricted part of the opening 26, that is, the upper end of the opening 26. It will thus be `seen that the inner surfacesof the bit 16, the welding 28, and the valve seat 22 dene a restricted non-circular throat at the lower end of the body 12, and that the throat 30 tapers upwardly progressively changing from being circular in transverse section to being roughly a truncated sector in transverse section at its upper end. The purpose of the restricted throat 30 will be presently set forth.

A valve plate 32, also having what may be described as the shape of a truncated sector is seated on the valve seat. A hinge strap 34 is riveted to the plate, as at 36, and at the minor or narrow end of the plate 32 is hinged tothe lower end of the mounting plate 38. The mounting plate 38 is, in turn, detachably secured to the body 12 by means of threaded fasteners 40 and 42 extending through countersunk smooth bores 44 in the body 12 and threadingly engaging the mounting plate 38. As shown in Figure 4, the fastener 42 extends into the body 12 to limit `opening movement of the plate 32' to the alternate position shown in dotted outlined at 46.

A jar construction designated generally at 48 is provided at `the upper end of the tubular body 12 for supporting the tubular body 12 for rotation about its longitudinal vertical axis. As best shown in Figure 5, the jar construction 48 includes a jar stem 50, the upper end of which is externally threaded and threadingly engaged in a socket formed at the lower end of a combined jar and connecting member 52, as at 54. A fixed jar or abutment 56 is secured as by welding to the jar stem 50 adjacent its lower end, and the lower end of the jar stem 50 has welded thereto a depending blade or cutter 58 having a transverse opening 60 therethrough. It will be understood that by merely extending a tool through the opening 60 the jar stem 50 may be secured against rotation and the member 52 easily disengaged from the upper end of the jar stem 50. For an illustration of the manner in which the jar stern 50 is mounted in the tubular body 12, attention is directed to Figures 2 and 3, wherein it will be seen that Vthe tubular body 12 is provided with a plurality of circumferentially spaced elongated slots 62. A spider construction is mounted in the slots 62 which includes a plurality of plates 64 seated in the slots 62 to extend radially inwardly into the body 12 to terminate in spaced relationship to each other, the plates 64 being secured to the body 12 as by welding. The jar stern is slidably and rotatably received between the inner ends of the plates 64. Reinforcing washers or abutments 68 loosely embrace the jar stem 50 and are secured as by welding or the like to the upper and lower ends of the plates 64 in spaced relation to the inner walls of the tubular body 12. It will be noted that the member 52 is spaced above the washers 68 and the jar 56 is spaced below the washers 68 so that relative vertical movement of the jar stem 60 and the body 12 is limited by engagement of the member 52 and the jar 56 with the washers 68. In order `to prolong the life of the jar construction 48, the present invention includes resilient cushion washers 70 and 72 secured to the member 52 and the jar 56, respectively. It should also be noted at this point that by virture of the washer 68 being spaced from the inner wall of the tubular body 12, fluids may freely pass vertically through the tubular body 12 past the jar construction 48, and that in addition, the jar stem 50 is journaled in the tubular body 12 in such a manner that the same will not sand up to prevent relative rotation as occurs in `other constructions of this general character.

The upper end of the member 52 is provided with a transverse opening 74 which receives the attaching eye 76 formed at the lower end of a conventional twisted strand steel cable 78. It will be understood that the cable 78 is of the type which will produce torsion when either placed under or released from tension. As thus far described, it will be appreciated that in raising and dropping the tool 10 by the use of the cable 78, the tubular body 12 will be rotated when the cable 78 is tensioned to raise the same by virtue of the frictional engagement of the lcushion washers 72 with the lowermost washer 68.

As clearly shown in Figures 1 and 2, commencing a considerable distance above the lower end of the tubular body 12, the latter is provided with a plurality of rows of vertically spaced and elongated slots 80 for a purpose to `be presently set forth. In addition, as clearly shown in Figures 2, 3 and 9, the upper end of the body 12 is provided with vertically elongated, circumferentially spaced clean-out openings 82 adjacent the jar construction 48. Closure plates are provided for removably closingthe clean-out `openings 82, such cover plates each consisting of an elongated plate 84 that is arcuate in transverse cross-section to be substantially of the same curvature as the outside surface of the tubular body 12. The plates84 are received within the openings 82, and have secured to their lower ends retaining lugs 86 which project downwardly to engage the inner surface of the tubular body 12. The straight transverse Ibar 88 is secured tothe inner side of each of the plates 84 at the end Vremote from the lugs 86, and the bars and the Y plates are provided with aligned openings 90 and 92,

respectively. Headed threaded fasteners 94 are disposed in the openings yand 92, and are rotatably retained therein by means of washers 96 that are secured to the heads of the fasteners 94 that extend radially to be received between the plates 84 and the bars 88, it being noted that the openings 92 are suciently large to permit access to the headed end of the fasteners 94 by means of a socket wrench or the like. Mounting bracket plates 98 are welded or otherwise suitably secured to adjacent plates 64 to provide additional lateral bracing for the plates 64, and are provided with smooth openings through which the inner ends of the fasteners 94 extend. Nuts 102 are threaded on the inner ends of the fasteners 94 and engaged against the plates 98 to secure the plates ,84 in positions closing the openings 82. lt will be appreciated that in lieu of the provision of the nuts 102, the openings 100 may be interiorly threaded so as to engage the fasteners 94.

It is thought that the use of the present invention will be readily understood. In drilling through formations above ground water level, a fluid level is maintained f within the hole sufficient to stand above at least the lowermost of the slots 80. It will thus be seen that the enlarged portion 18 of the bit 1d will cut a hole 104 through the formation 106 slightly exceeding in diameter the outside diameter of the tubular body 12. Upon, downward movement of the tool 10, the valve plate 32 is forced upwardly by uid pressure to permit the flow of fluid upwardly into thetubular body 12. Upon raising the tool 10, the valve plate 32 is closed by iluid pressure so that the iluid may now ow through the inside of the tubular body 12, outwardly through the slots 80, downwardly in the annular space in the hole104 surrounding.

the tubular body 12, and thence upon the next downward movement of the tool upwardly through the valve into the interior of the tubular body 12. While prepared muds or simply surface soil may be'added to water and placed in the tool 10, it has been found in practice that the mere working of the tool in water will provide a drilling Huid of sufficient consistency to produce the desired effect of plastering or mudding the side walls of the hole 104 during the circulation of thedrilling uid thereagainst. As is well known, the Plastering or mudding of the walls ofa well hole will seal the same against cave-ins or the like, and it is by virtue of this operation or function of the present invention that the use of casing or drive pipe through structurally weak, or loose sanded formations will prevent cave-ins. f

In drilling in formations below ground water level, it is desired to use hydrostatic 'pressure within the hole 104 to oppose the hydraulic forces existing in the formations that tend to produce cave-ins in the well hole, and, accordingly', during'such drilling a iluid level is maintained within the hole that is above the ground Water level existing in the formation or at least at a sufficiently high level to prevent cave-ins. In all other respects, the drilling below ground waterlevel' is accomplished in substantially the same manner as above ground water level, and the drilling uid circulates in the same mannerA and tends to cement or seal the walls of thek well hole by Plastering or mudding the same.

It will be evident that in using a hole drilling tool of this type the tool 10 will tend to form a core which will extend upwardly into the lower end of the tubular body 12 that would tend to interfere seriously with the operation of the valve at the lower end of thebody; however, in the use of the present invention, the turning effect on the tool produced by the twisted cable 78 coupled with the shape of the upwardly tapered, 'noncircular throat at the lower end of the body below the valve cooperate to wear down the size of such a core and to break oif the same into chunks which may pass upwardly through the valve seat 22 Without interfering with the operation of the valve plate 32. In addition, it should be noted that the chunks of material broken olf by the restricted throat will be of small enough size to pass upwardly through the valve without interfering with the operation of the same, but will'also be large enough so that upon raising the tool 10 to the surface, the driller may, upon inspection of the same, determine with accuracy the character of the formation through which the tool is passing. V

'It should also be noted that in the event the slots 80 become congested with material within the tubular body 12 to such an extent that the circulation of the drilling fluid would be reduced, the drilling fluid will be free to pass upwardly through the tubular body 12 to the exterior of the tool 10 through the passages afforded between the plates 64 and between the washer 68 and the inner surfaces of the tubular body 12, and in fact, such an operation or function of the tool has proven so satisfactory that the slots 80 may be dispensed with entirely if desired. In addition, the circulation of the drilling fluid may, under certain adverse conditions, be further expedited by the removal of the plates 84 so that the 6 1 l 7 drillinguid circulation may pass through the openings 82 as well as upwardly past the jar construction 48.

It will befurther appreciated that the tool 10 is capable; of dual functions, that is, the tool 10 may vnot onlyvbe used as a drill and a drilling Huid pump, but mayalsof be used as a bail bucket by virtue of the spacing of the lowermost of the slots 80 above the valve. p

The present invention is particularly well adapted for bringing in wells in loose sanded formations. By. the expression loose sanded formations it is meant through-- out this specification any formation which is structurally weak and susceptible to caving in to the well hole through the action ofvhydraulic forces obtaining therein. The newly discovered method of completing wells in loose sanded formations resides in drilling into `such a loose sanded formation while maintaining a fluid levely in the hole suiciently high to prevent the caving in of the formation. Generally speaking, maintaining a uid level in the hole above the top of the loose sanded formation or above the ground water level therein is sufficient to prevent the caving in of the formation. After the wellI is drilled to such a depth that it is believed that the samewill be capable of producing water in the quantities desired, the present invention contemplates a procedure whereby this fact may be ascertained with certainty prior to the setting of thel casing, so that if the well has not f been drilled su'iciently deep, the sarnemay be deepened to the necessary extent prior to even going to the time and labor consuming procedureiof setting the casing.

. distance below the ground water level in the loose sanded mation, any further cave-in.

formation, so that by knowing the level at which the cave-in occurred, the driller is readily apprised of the approximate location of the ground water level in the' formation.

Figure 10 indicatesthe foregoing operation in which the well bore has been drilled to a depthestimated to be,`

somewhat below the level of ythe ground Water. Any cave-in is of course prevented by the drilling fluid in the well bore.

As shown in Figure 11, the drill tool is lifted a suicient distance to be above the water level and any cave-in to avoid being buried thereby. Then the drilling fluid level at the well bore is lowered, permitting the hydrot static head of the water in the formation to cave in the Well bore as shown in Figure l1 by the caved-in material A.

If the estimate as to the.. ground water level was incorrect, so that no cave-in occurred, the drilling fluid would be again applied an-d the drilling continued to a greater depth. This would be repeated until a depth was reached beneath the water level, whereupon a cave in as shown in Figure ll would be effected. The cave` in would indicate approximately the water level of the water producing formation, and with this level now ascertained the requisite depth to which the well bore must be drilled to give the desired depth of water in the well can be easily determined.

Immediately upon the occurrence of the cave-in, and so that the cave-in will be minimized and not creepy upwardly in the hole, the driller raises in any conventional .manner the Huid level within the hole, and then drills through the caved-in material in the hole. This next step is illustrated at Figure l2 wherein it will be noted that the well bore has been lled in` above the caved-in portion fby mud B, and the drilling fluid level restored in order to prevent, by its pressure on the for- The driller then drills the: bottom of the hole' to whatever depth is required to 7 produce the desired feet of water head of the ground water levelabove the bottom of the hole, it being obvious that if the wellhole was already sufciently deep, no further drilling \vill be required',and the casing may then be set. It has also been found by experience that a cavein produced under the conditions set forth above will notA cause caved-in material to f-all clear to the bottom of the hole, but such caved-in materialonly extends across the hole at the level of the cave-in so that the same may be Yreadily drilled out withoutrequiring any redrilling below the level of thecave-in. Obviously, if no cave-in occurs at all during the lowering in any suitable manner of the level: ofv the tluid within the hole, the hole has not been drilled to a su'icient depth below ground water level, or may in f-act not even be down to ground water level, under which circumstances the driller will deepen the hole a considerably greater depth and then repeat the above steps. f

The completion ofthe drilling operation is indicated in Figure 173, with the wellbore now drilledV through the `mud B to the required depth to complete thewell bore. Thereafter, the casing C-is inserted asj in `Figure 14, the drill tool is `removed and the casing is gravelled as at G and the well is nowcompleted.

The tool 10 is wellsuited for the abovemethod for the reason that the tool may `be used both for lowering the uid level within the holeas well as Vfor raising the same inasmuch as the same -serves the auxiliary funetion of serving as a bail bucket. The advantage in the use of the tool 10` in raising the fluid level in the hole resides in the fact that the fluid may be lowered' gently into the hole rather than simply poured into the same, which latter procedure would tend to wash down the sides of the hole and thus induce the possibility of a cave-in at a higher levelwithin the hole. l

From the foregoing, the construction and operation of the device will be readily understood and further explanation is believed to be unnecessary. However, since numerous modications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction shown and described, and accordingly, all suitable modificationsand equivalents may Abe resorted to, falling within the scope f; the appendedclaims.

Whatlis claimed as new is as follows:

1. A method for completing in a loose sanded for mation a water well having a predetermined standing water level therein which comprises; drilling an open hole into a loose sanded formation below the ground water level, maintaining during said drilling a uid level in said hole above said ground water level by introducing fluid as required into said hole, progressively lowering the fluid level by withdrawing fluid from the hole until the fluid level is below the ground water level and a cave-in occurs and thereby ascertaining the water level in the loose sanded formation adjacent the hole, raising the fluid level above said ground water level by again introducing fluid into said hole, thereafter and while maintaining said fluid level above said ground water level drilling until` the hole is extended to the desired depth belowy said ascertained ground water level.

2. A method for completing in a loose sanded formation a water well having a predetermined standing water level therein which comprises; drilling an open hole into a loose sanded formation below the ground water level, maintaining during said drilling a fluid level in said hole above said ground water level by introducing fluid as required into said hole, progressively lowering the fluid level by withdrawing fluid from the hole until the iluid level` is below the ground water level and a cave-in occurs and thereby ascertaining the water level in the loose sanded formation adjacent the hole, raising the fluid level above said ground water level by again introducing ucl into said hole, thereafter removing the caved-in material from said hole and while maintainingsaid fluid level above said ground water level drilling until the hole is extended to the desireddepth below said ascertained ground water level.

3. A `methodfor completing in a loose sanded formation a waterwell having a predetermined standing water level therein which comprises; drillingl annopen hole into a loose sanded formation below the .ground waterlevel, maintaining dur-ing said drilling a fluid level in said hole above said ground water level by introducing- Huidr as required into said hole, then raising thev drilling tool Vin thehole above the ground waterlevel, progressively lowering the fluid level by withdrawing fluid from the holeuntilA the fluid level is below the ground water level and a cave-in` occurs and thereby ascertaining` the water level. inV the loose sanded formation adjacentthe hole, raising the fluid level above said ground waterlevel by again introducing fluid into said hole, thereafter lowering the drilling `tool into drilling position and while-maintainingsaid fluid level above said ground water level drilling until the hole is extended to the desired-,depthbelowsaid ascertained ground water level.

4. A methodV for completing in a loose sanded formation a water well having apredetermined` standing water level `therein which comprises; drilling an open hole into a loose sanded formation below the ground water level, maintaining during said drilling a tluid level in said hole above said ground water level by introducing fluid as required into said hole, progressively lowering the uid level by withdrawing fluid from the hole until the fluid level is below the ground water level and a cave-in occurs and thereby ascertaining the water level in the loose-sanded formation adjacent the hole, preventing upward creeping of the cave-in by raising the fluid level above said ground water level by again introducing uidinto said hole, thereafter and maintaining said fluid level above said ground water level drilling until the hole is extended to the desired depth below said ascertained ground water level.

5. A method for completing in a loose sanded forma.- tion a water well having a predetermined standing Water level therein whichcomprises; drilling an openhole into a loose sanded formation below the ground water level, maintaining during said drilling a fluid level in said hole above said ground water level by introducing iluid as required linto said hole, progressively lowering the fluid level by withdrawing fluid from the hole until the fluid level is below the ground water level and a cave-in occurs and thereby ascertaining the water level in the loose sanded formation adjacent the hole, raising the fluid level above` said ground water level by again introducing fluid into said hole, thereafter and while maintaining said fluid level above said ground water level drilling until the hole is extended to the desired depth below said ascertained ground waterlevel, and nally positioning a casing in thehole to the bottom thereof and thereby preventing further caving in of the loose sanded formation.

6. A method of completing a water well in a loose sanded formation, comprising `the steps of drilling an open hole into a loose sanded formation'below the adjacent ground water level of said formation, maintaining during said step of drilling a uid level in the hole above said ground water level by introducing fluid into said hole as required, thereafter progressively lowering the iluid level in the; hole until it falls below the ground water levelanda cave-in occurs, then preventing enlarging of the cave-in by again introducing uid into the hole ,and raisingthe uid level above said ground water level and thereafter drilling the hole to completion.

7. A method of completing a water well in a loose sanded formation, comprising the steps of drilling an openhole into a loose sanded formation below the adjacent ground water level of said formation, maintaining during said step ofdrilling a fluid level inthe hole above said ground water level by introducing uid into said hole as required, then raising the drilling tool in the hole and thereafter progressively lowering the fluid level in the hole unt-i1 it falls below the ground water level and a cave-in occurs, then preventing enlarging of the cave-in by again introducing iluid into the hole and raising the uid level above said ground water level and again lowering the drilling tool into drilling position and thereafter drilling the hole to completion.

References Cited in the file of this patent UNITED STATES PATENTS Phillips et al. Nov. 11, 1873 Murray et al Nov. 17, 1914 Swan May 15, 1923 Evans et al. Feb. 9, 1926 Gray July 8, 1952 Wilcox Oct. 18, 1955 

6. A METHOD OF COMPLETING A WATER WELL IN A LOOSE SANDED FORMATION, COMPRISING THE STEPS OF DRILLING AN OPEN HOLE INTO A LOOSE SANDED FORMATION BELOW THE ADJACENT GROUND WATER LEVEL OF SAID FORMATION, MAINTAINING DURING SAID STEP OF DRILLING A FLUID LEVEL IN THE HOLE ABOVE SAID GROUND WATER LEVEL BY INTRODUCING FLUID INTO SAID HOLE AS REQUIRED, THEREAFTER PROGRESSIVELY LOWERING THE FLUID LEVEL IN THE HOLE UNTIL IT FALLS BELOW THE GROUND WATER LEVEL AND A CAVE-IN OCCURS, THEN PREVENTING ENLARGING OF THE CAVE-IN BY AGAIN INTRODUCING FLUID INTO THE HOLE AND RAISING THE FLUID LEVEL ABOVE SAID GROUND WATER LEVEL AND THEREAFTER DRILLING THE HOLE TO COMPLETION. 